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Abstract:

Hydrology is a key factor in the terrestriallandscape that connects upland and riparian ecosystems
to streams. Hydrological connectivity through the catchment
and along the stream network influences not only
the timing and the magnitude of terrestrial inputs to
stream ecosystems, but also regulates streammetabolism
and biogeochemical cycling. In mediterranean climate
regions (med-regions), there is a marked seasonal alternation
of dry and wet periods, and streams experience a
wide range of hydrological conditions from floods to
droughts. Moreover, nutrient dynamics in med-streams
are highly variable within the year and between years
compared to temperate streams. In this review, we
explore how seasonal changes in hydrological connectivity
and hydrological extremes affect nutrient cycling
and transport at different spatial scales in med-catchments.
We show that during the dry period, the stream
network contracts more severely in med-catchments than
in temperate catchments. During the contraction phase,
upland-stream disconnection decreases nutrient supply
from terrestrial ecosystems, while stream fragmentation
increases the spatial variation of stream nutrient concentrations.
Moreover, the precipitation regime typical of
med-regions (with irregular distribution of precipitation
and episodic large rainfall events) decreases the ability of
terrestrial and aquatic biota to retain nutrients and favours
nutrient export to downstream ecosystems. Altogether,
this hydrological setting confers to med-streams a
characteristic temporal pattern in stream nutrient dynamics
that is analogous to a particular biogeochemical
heartbeat with higher amplitude, variation and unpredictability
than that observed in temperate streams.